Noise reduction device for submarines



June 28, 1960 M. w. LINDMAN uoxsa REDUCTION .DEVICEFOR SUBMARINES FiledAug. 29, 1957 3%?! was 395 INVENTOR v v1ZW'f/J Aka mew,

.BY /'6 A.

ATTORNEYS United States Patent 2,942,681 NOISE REDUCTION DEVICE FORMorris w. Lindman, Adelphi, Md, assignor m the United States of Americaas represented by the Secretary of the Navy Filed Aug. 29, 1957, Ser.No. 681,147

7 Claims. (Cl. 181-33) (Granted under Title 35, US. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This invention relates to sound absorbing systems and particularly tosystems for absorbing structure-borne noise.

More particularly, this invention relates to the reduction of noisetransmission from submarines, minesweepers and other vessels to ambientwaters.

With submarines, for example, inherently noisy machinery hereinafterreferred to as noise-producing machinery, is mounted on resilientmountings which in turn are supported on the structural rings thatreinforce the pressure hull of the ship. With present submarines, alarge part of the structure-borne noise of the machinery is transmittedthrough the mounting and hence to the reinforcing rings, the pressurehull, and to ambient waters. This transmission of noise to surroundingwater is extremely dangerous in that the presence of the submarine mayreadily be detected from the noise by known detecting devices.

Therefore, a broad object of the present invention is to reduce thetransmission of structure-borne noise to ambient media.

Another object of this invention is to absorb structureborne noise.

A further object of this invention is to provide a path of highlyefficient acoustical power transmission for the transmission of absorbednoise from a source to a place of absorption.

A more specific object of this invention is to provide a plurality ofstructural sound-transmitting paths of highly efiicient acoustical powertransmission from inherently noisy machinery, and of converging suchpaths in a sound absorbing material.

Briefly, in applying the instant invention to the hull of a submarine,for example, a plurality of metal, noisetransmitting rings, one for eachof the structural reinforcing rings, is mounted between the reinforcingrings and the interior of the pressure hull. The noise-transmittingrings are interconnected by a plurality of spaced metal bars, all ofwhich bars converge into a single bar or rod within and spaced from thestern of the ship. The single bar is embedded within a substantialvolume of sound absorbing material and is equipped with a plurality ofspaced disks of various natural frequencies, which disks are looselyembedded within the sound absorbing material.

The plurality of sound-transmitting rings and the plurality of bars makeup a squirrel-cage, the material of which is of higher specific acousticimpedance than that of the rest of the ships structure, thereby forminga path, or rather a plurality of paths of least resistance that convergeinto a single path, which single path is surrounded by a relativelythick bedding of sound absorbing material. In other words, thesound-transmitting rings 2,942,681 Patented June 28, 1960 and bars thatmake up the squirrel cage should be of a material such that itsimpedance matches the output impedance of the driver better than theimpedance of the hull or casing, thereby forming a plurality of paths ofhighly efiicient acoustical power transmission for transmitting noisefrom the machinery to a concentration region remote from the machinery;a structure which conducts more vibrational energy away from themachinery than does the hull or casing. The sound-transmitting rings areinsulated from the metal of the pressure hull and the bars arepreferably coated with a highly dissipative material, such as a suitableplastic, to minimize their vibration between the rings and radiation tothe hull.

Thus, there is provided a plurality of paths for transmittingstructure-borne noise from inherently noisy machinery to a concentrationarea wherein the noise is smothered and suppressed in a substantialvolume of sound absorbing material. As used herein, noise is intended torefer to structure-borne noise" and is not intended to include noisethat is transmitted or radiated through air. The squirrel-cage of theinstant invention is not intended to be, and preferably is not, astrength member for the ship.

The invention, together with the above and other obljects andadvantages, is set forth in more technical detail in the followingdescription and accompanying drawing wherein the single figure is aschematic perspective view, partly in section, of the stern or aftportion of a submarine, illustrating a preferred embodiment of theinvention.

Referring now to the drawing, reference numeral 10 designates thepressure hull of a submarine, to the interior of which is securelymounted a plurality of reinforcing rings 12, only two of which rings areshown in the drawing. As is customary, various noise-producing machinery(not shown) is mounted on the reinforcing rings.

In accordance with this invention, a plurality of metal,noise-transmitting rings 14, one for each of the reinforcing rings, aremounted between the reinforcing rings and the interior surface of thepressure hull. The rings 14 are in metal-to-metal contact with thereiifiorcing rings, but are insulated by suitable means, not shown, fromthe pressure hull. A plurality of metal bars or straps 16 are attachedto the rings 14 and converge in a region A, from which extends a singlemetal bar or rod 18, on which rod is located a plurality of disks 20 ofvarious natural frequencies. The region of convergence, A, of bars 16,the rod 18 and the disks 20 are located within and spaced from the sternof the ship, which space is filled with sound absorbing material, 21,which may be a mineral wool, or glass fiber batting or the like. Thesound absorbing material is confined within the stern by a partition orbulkhead 22, which partition is provided with a plurality of openings 24for passage of the bars 16 therethrough and out of contact with thepartition.

The sound-transmitting rings 14 and bars 16 that make up thesquirrel-cage, and the rod 20 are each formed of the same material, amaterial having a higher specific acoustic impedance than that of therest of the ships structure. The material of the squirrel cage is suchthat its impedance matches the output impedance of the driver(machinery) better than the impedance of the hull or casing, therebyforming a structure which conducts more vibrational energy away from themachinery than does the hull or casing. For steel ships, this materialmay be nickel or steel with a high nickel content. In wooden ships, suchas mine sweepers, almost any non-magnetic metal may be used. So as tominimize vibration of the bars or separate elongated, rodlike metalsound conducting members 16 between the rings 14, the bars are coatedwith a highly dissipative plastic material, such as polyethylene orpolystyrene, the latter being preferred because I of its ability towithstand somewhat higher temperature without distortion.

-Thus it is seen, in accordance with the illustrated embodiment of theinvention, structure-borne noise is transmitted from inherently noisymachinery, mounted on or supported by the reinforcing rings, by themembers of the squirrel-cage, to a region within the stern of the ship,wherein the noise is smothered in the sound absorbing material.

The invention is herein illustrated as applied to noiseproducingmachinery of a submarine or the like. The invention may, however, beapplied with equal facility to other noise-producing machinery. Itshould therefore be understood that the foregoing disclosure relates toonly a preferred embodiment of the invention and that numerousmodifications or alterations may be made therein without departing fromthe spirit and scope of the invention as set forth in the appendedclaims.

What is claimed is:

1. A submarine or the like comprising a metallic hull, a skeletonmachinery supporting frame on the interior of said hull, soundinsulating means between said frame and said hull, and sound attenuatingmeans adjacent a terminal portion of said hull and acousticallyinsulated therefrom, said frame being operatively connected to saidattenuating means.

2. The combination of claim 1 in which the sound attenuating meanscomprises a plurality of laterally spaced metal bars, each of whichconducts more vibrational 4 energy away from said machinery supportingframe than does said hull.

3. The combination of claim 1 in which the sound attenuating meanscomprises a network of sound conducting bars and rings, and soundabsorbing material encompasses the bars and rings.

4. The combination of claim 1, including a. network formed of soundconducting bars and rings, and sound absorbing material encompassing thebars and rings.

5. The combination of claim 1, which includes a central rod, a pluralityof sound dissipating disks mounted in spaced relation on said rod andembedded within the sound absorbing material.

6. The combination of claim 1, which includes inherently noisy machinerydisposed within said hull, a network formed of sound conducting bars andrings, and sound absorbing material encompassing said bars and rings.

7. The combination of claim 6 in which the sound absorbing material ismineral wool batting.

References Cited in the file of this patent UNITED STATES PATENTSStewart et al Jan. 17, 1956

